After 4-6 minutes of cerebral hypoxia, brain cells begin to suffer irreversible damage and their functions are affected, causing whole brain functional impairment, a process that is almost irreversible and can also be called diffuse damage. The recovery of the effect of any drug on brain cell apoptosis is of little effect, and only timely correction of ischemia and hypoxia can correct the underlying state of brain death. Cerebral ischemia and hypoxia, as well as coma, loss of brainstem reflexes and loss of voluntary breathing, are all manifestations of brain death. If effective relief is not available, apoptosis of brain cells can begin after 4-6 minutes of hypoxia, and brain death will occur if it continues to progress. Brain death is an irreversible process of loss of function of the whole brain, including the brainstem, and is different from the vegetative state. In the vegetative state, brainstem function exists, while coma is only due to sudden impairment of cerebral cortex function or total inhibition, and patients can have voluntary breathing, heartbeat and brainstem reflexes. Patients with brain death must not have spontaneous respiration and are irreversible. All causes of comprehensive cerebral ischemia and hypoxic changes can cause brain death, such as massive cerebral infarction, cerebral hemorrhage, craniocerebral trauma, drowning, respiratory and cardiac arrest, etc.